In a dual-chamber cardiac pulse generator, it is desirable not to detect a far-field QRS Signal and mistake it for being a P-wave. In a bradycardia pacemaker where detection of high atrial rate is not necessary, this is avoided by keeping the atrial detector refractory during periods where far-field QRS or other unwanted signals might be present. One example of such an atrial refractory period is the so called xe2x80x9cTotal Atrial Refractory Periodxe2x80x9d (TARP) which starts at an atrial event and, by having an appropriate value, remains in effect until a reasonable amount of time after the following ventricular event. Another example is keeping the atrial detector refractory until the following ventricular event and then starting a xe2x80x9cPost Ventricular Atrial Refractory Periodxe2x80x9d (PVARP) having a reasonable duration. However, in devices where detection of high atrial rate is necessary, examples being ICDs and also pacemakers implementing mode switching as a result of high atrial rate, the mentioned TARP and PVARP may result in undersensing of a true atrial signal, thereby compromising the response from the device. It can be mentioned here that the purpose of the PVARP (or the portion of the TARP that remains after a ventricular sensed or paced event) is to prevent initiation of the so called Pacemaker Mediated Tachycardia (PMT) by avoiding sensing of the retrograde conduction by the atrial detector (which in an atrial tracking mode would lead to triggering of a ventricular pacing pulse).
The invention allows use of short atrial refractory periods when attempting to detect high atrial rate (if prevailing).
A scheme aimed at detecting maximum possible amount of true atrial signal while avoiding far-field QRS and other unwanted signal is disclosed. The innovation lies in the avoidance of the far-field QRS. Other unwanted signals, e.g. other parts than the P-wave of the atrial signal, can be handled by an appropriate atrial refractory period which need not be very long, thus allowing detection of a high true atrial rate.
Thereby a mechanism is implemented, so that the shortest possible Short Atrial Refractory Period (SARP) and Post Ventricular Short Atrial Refractory Period (PVSARP) can be used, thus enabling detection of high rate atrial rhythms.